Power supply circuits have the advantages of low weight, small size, low power consumption; and have been widely used in various electronic devices, such as liquid crystal display (LCD) monitors and televisions.
A typical power supply circuit includes a bridge rectifier circuit for converting an external alternating current (AC) voltage to a high level direct current (DC) voltage, a filter circuit for filtering the high level DC voltage to a stable DC voltage, and an inverter circuit for converting the stable DC voltage to a desired low level AC voltage. In order to maintain the stable DC voltage, the filter circuit generally needs a filter capacitor with large capacity.
When an electronic device using the power supply circuit is powered off, the power supply circuit is turned off. Due to its large capacity, the filter capacitor may store a large quantity of electric energy. This may cause the inverter circuit to work in an abnormal state after the power supply circuit is turned off. As a result, the inverter circuit may be damaged or completely broken. Thus the reliability of the power supply circuit is somewhat low.
What is needed is to provide a power supply circuit that can overcome the above-described deficiencies.